Conventional lead acid battery plates include a positive electrode (PbO.sub.2 plate) and a negative electrode (Pb plate) immersed in a sulfuric acid electrolyte and having a separator interposed therebetween. As a means of improving the ease of manufacture of such batteries, a variety of conductive additives have been proposed for incorporation into the plates. Lead dioxide has been proposed as an additive for paste mixtures containing tetrabasic lead sulfate, as described in Reich, U.S. Pat. No. 4,415,410, issued Nov. 15, 1983. Lead dioxide has also been formed in battery pastes by a reaction between lead monoxide and a persulfate salt (Reid, U.S. Pat. No. 2,159,226, issued May 23, 1939) or with ozone (Parker, U.S. Pat. No. 4,388,210, issued June 14, 1983, and Mahato et al, U.S. Pat. No. 4,656,706, issued Apr. 14, 1987). Lead dioxide enhances positive plate formation but provides no substantial advantages in the resulting battery because it participates in the positive plate reaction. During charging of the battery, lead sulfate is converted into lead dioxide, and the reverse reaction occurs during discharge.
Battery plate grids comprising a composite article on which a flowable plastics material is molded to engage portions of a conductive material, such as lead or a lead alloy, are also known. Buckethal et al, U.S. Pat. No. 4,118,553 issued Oct. 3, 1978. Also known is a lead-acid rechargeable cell having a positive electrode wherein a titanium alloy replaces lead as the supporting member for the active lead peroxide and is covered with a nonpolarizing film of gold or other suitable material. See, Ruben, U.S. Pat. No. 3,615,831 issued Oct. 26, 1971.
Carbon has been used as a lead-acid paste additive, and has been used in combination with plastic materials in electrodes for bipolar lead-acid batteries, as described in Biddick, U.S. Pat. No. 4,098,967, issued Jul. 4, 1978. Carbon, however, is not stable as a positive electrode material because it tends to oxidize. Thus, bipolar electrodes solely utilizing carbon as the conductive filler are not generally satisfactory for long term use.
Unitary plate electrodes comprising fiberglass coated with tin dioxide, lead dioxide, and a thin film of lead or graphite filled resin are described in Rowlette et al, U.S. Pat. No. 4,547,443 issued Oct. 15, 1985. That use does not, however, suggest the uses of transition metal conductive oxides in the manner described herein
The present invention involves the use of conductive oxides, preferably those of titanium, tungsten, molybdenum, vanadium and niobium. Certain oxides of these transition metals exist or can be prepared in a non-conductive state. Reduction of these non-conductive oxides, such as in a hydrogen atmosphere, at elevated temperatures, creates a conductive class of materials whose use in batteries or electrodes as described herein has not heretofore been recognized.
Certain conductive metal oxides have been used in applications, for example, in polymeric compositions for electrical components as described in Penneck et al, U.S. Pat. No. 4,470,898, issued Sept. 11, 1984, and in corrosion-resistant coatings as described in Tada, U.S. Pat. No. 4,352,899, issued Oct. 5, 1982.
Voss et al, in U.S. Pat. No. 3,096,215 issued Jul. 2, 1963 discloses the use of a sintered titanium dioxide electrode, impregnated with silver, as an auxiliary electrode for eliminating gases formed during operation of the battery. The electrode is formed with a cavity communicating with a gas space of the battery so that gas produced during formation or discharge can be absorbed. The auxiliary electrode is coupled electrically to the positive or negative plates of the battery, depending on which electrode is causing the problem gas generation.
Certain metal oxides have also been suggested for use in fuel cells to serve as substitutes for the more expensive platinum as a catalyst material See, Nestor, U.S. Pat. No. 3,480,479 issued Nov. 25, 1929 (a molybdenum oxide mixed with tungsten disulfide); Broyde, U.S. Pat. No. 3,544,378 issued Dec. 1, 1970 (a rare earth tungsten oxide M.sub.x WO.sub.3 where x is between 0 and 1 and M is a rare earth element).
An oxygen reducing negative active material for a storage cell which includes a molybdenum oxide having an average valency between 4 and 6 is discussed in Gabano et al, U.S. Pat. No. 3,871,917 issued Mar. 18, 1975. The oxide is supported by mechanical compression. A conductive body (e.g. graphite) and binding agents may be employed. The material is used with conventional positive electrode systems (i.e., PbO.sub.2,PbSO.sub.4 /H.sub.2 SO.sub.4,H.sub.2 O.
Further, the use of bulk titanium oxide having the formula TiO.sub.x where x is 1.55 to 1.95 has been suggested for electrode use in electrochemical cells. See, Hayfield, U.S. Pat. No. 4,422,917 issued Dec. 27, 1983. Solid, bulk titanium oxide materials are discussed for electrode applications including storage batteries, bipolar cells for chlorate production, etc.
Tin dioxide (SnO.sub.2) has also been suggested as a coating for fiberglass strands of unitary electrodes. See, for example, Rowlette et al, U.S. Pat. No. 4,547,443, issued Oct. 15, 1985 This coating has proven somewhat useful, but it fails to completely meet the need for a conductive additive which is economical, enhances plate formation and also improves the properties of the resulting lead-acid battery.
The present invention provides novel electrodes used in lead-acid batteries which are not appreciated by the foregoing art and which overcome the deficiencies of the aforementioned systems.